1. Field
The present disclosure relates to a sheet transporting device having a structure in which a curved transport path is provided downstream in a sheet transport direction from a merging section where a plurality of transport paths, which are formed by transport guides for transporting sheets, merge; a document feeder including the sheet transporting device; and an image forming apparatus including the document feeder.
2. Description of the Related Art
Hitherto, a sheet transporting device and an image forming apparatus including a movable transport guide that is rotatably provided at a merging section where a plurality of transport paths merge have been disclosed (refer to, for example, Japanese Unexamined Patent Application Publication No. 2004-354422 (PTL 1)).
The sheet transporting device is provided with a first transport path for sheets that are sent out from a sheet-feed cassette, a second transport path for sheets that are sent out from a manual feeder, a third transport path for transporting sheets during duplex printing, and a pair of register rollers that rotate while they form a nip region. The transport paths form a transport path merging section by merging into one path at a location that is upstream in a transport direction of the pair of register rollers for causing an end portion of an image that is formed on a photoconductor drum and a leading end portion of a sheet to be synchronized with each other.
The first transport path is formed between a first stationary guide and a second stationary guide. The second transport path is formed between the second stationary guide, a third stationary guide, and the movable transport guide (provided on a line of extension of the third stationary guide). The third transport path is formed between the third stationary guide, the movable transport guide (provided on the line of extension of the third stationary guide) and a fourth stationary guide.
In this structure, the movable transport guide is movable for guiding sheets to the nip region between the pair of register rollers, and an end portion of the movable transport guide is formed so as to contact the first stationary guide at a location near the nip region.
According to this structure, even if a sheet is curled, it is possible to properly guide the sheet to the nip region while reducing the curl by the movable transport guide.
However, as shown in FIG. 15, in a sheet transporting device having a structure in which a curved transport path 143 is provided downstream in a sheet transport direction Y11 from a merging section P11 where a plurality of transport paths (for example, two transport paths, such as a transport path 141 and a transport path 142), which are formed by transport guides for transporting sheets, merge, the following occurs. That is, a sheet M that is transported to the curved transport path 143 from the merging section P11 via the lower transport path 142 that is disposed at a side of the curved transport path 143 (that is, at the same side in a curving direction in a height direction) is transported such that its leading end portion M1 is transported into the curved transport 143 before its trailing end portion M2 passes the merging section P11.
Therefore, the sheet M in this state of transportation is in a state in which its leading end portion M1 is curved into a U shape by the curved transport path 143. When, in this state, the trailing end portion M2 of the sheet M moves to the merging section P11 from the transport path 142, flexing force of the sheet M that passes the interior of the curved transport path 143 causes the trailing end portion M2 of the sheet M to jump up in a direction opposite to a flexing direction of the sheet (indicated by an alternate long and two short dashed line in FIG. 15).
At this time, at the merging section P11, a large height difference D11 exists between a transport guide 142a at the upper side of the transport path 142 and a transport guide 141a at the upper side of the merging section P11. Therefore, the trailing end portion M2 of the sheet M jumps up by a large amount and forcefully strikes the transport guide 141a at the merging section P11. This causes a striking sound (unpleasant sound) to be generated. In particular, when a sheet is stiff, the sheet jumps up more strongly. This causes a louder striking sound (unpleasant sound) to be generated.
This problem is caused by the fact that the sheet is curved along the curved transport path because, when the trailing end portion of the sheet moves to the merging section from one of the transport paths, the leading end portion of the sheet is being transported in the curved transport path that is at a closest location at the downstream side in the transport direction.
PTL 1 discloses the technology of providing a movable transport guide for reducing a curl of a sheet. However, the transport path structure in PTL 1 and the transport path structure in FIG. 15 above differ from each other (that is, in PTL 1, a curved transport path does not exist near the downstream side of the merging section). Therefore, the problem that exists in the transport structure shown in FIG. 15 does not exist in the transport structure in PTL 1. Consequently, even if the movable transport guide described in PTL 1 is applied as it is to the transport path structure shown in FIG. 15, the problem that exists in the transport structure shown in FIG. 15 still exists.